Path to ie.css is incorrect when using a subtheme

Hi,

I'm using sky as a base theme. When I look at the path to ie.css in my html source it's set as:

<link type="text/css" rel="stylesheet" href="http://www.mydomain.co.uk/sites/all/themes/MY_SUB_THEME/css/ie.css?llqryj" media="all" />

Where MY_SUB_THEME should really be sky I would think?

This line in sky's template.php is using global $theme_path:

/**
 * Override or insert vars into the html template.
 */
function sky_preprocess_html(&$vars) {
  global $theme_path;

  // Add conditional CSS for IE7 and below.
  drupal_add_css($theme_path . '/css/ie.css', array('group' => CSS_THEME, 'browsers' => array('IE' => 'lte IE 7', '!IE' => FALSE), 'preprocess' => FALSE));
}

I know I could copy the ie.css to my theme folder but that's the whole point of using a base theme. Either this should be hard set get the path to sky, or a comment put in the readme to tell people they need to copy the ie.css to their subtheme folder?